1. Field of the Invention
The present invention relates to a display apparatus having an electroluminescence element in each pixel, and particularly to such a display apparatus having a function of correcting a display variation.
2. Description of the Related Art
Electroluminescence (hereinafter referred to as “EL”) display apparatuses in which an EL element which is a self-emissive element is employed as a display element in each pixel are expected as a flat display apparatus of the next generation, and are being researched and developed.
After an EL panel is created in which an EL element and a thin film transistor (hereinafter referred to as “TFT”) or the like for driving the EL element for each pixel are formed on a substrate such as glass and plastic, the EL display apparatus is subjected to several inspections and is then shipped as a product.
In a current active matrix EL display apparatus having a TFT in each pixel, a brightness unevenness occurs among the EL elements because of display unevenness caused by the TFT, in particular, a variation in the threshold value Vth of the TFT, which is a major cause of reduction in yield. An improvement in the yield of the products is very important, and, thus, reduction in the display defect and display unevenness (display variation) by improving an element design, a material, a manufacturing method, or the like is desired. Attempts have been made, for example, as described in JPA 2005-316408 (hereinafter referred to as “Reference Document 1”), in which, when a display unevenness or the like occurs, the display unevenness is corrected so that the panel is made a non-defective panel.
In the Reference Document 1, the EL panel is caused to emit light, variation in brightness of the pixels is measured, and a data signal (video signal) to be supplied to each pixel is corrected. In addition, as another method, a method is proposed in which a circuit which corrects the variation of Vth of an element driving transistor which controls a current to be supplied to the EL element is provided in each pixel.
The method of measuring the brightness variation by causing the EL panel to emit light and capturing an image of the emission with a camera as described in Reference Document 1 cannot be conducted after shipment, such that this method does not enable execution of corrections with respect to changes of the panel over time or the like. Furthermore, when a resolution of the EL panel is increased and a number of pixels in the EL panel is increased, a number of the measurement and correction target becomes large for measuring the brightness variation for each pixel, and, thus, an increase in the resolution of the camera, an increase in capacity of a storage of correction information, etc. are required.
Moreover, even when the circuit element for compensating Vth is not to be incorporated, it is highly desired to correct the display unevenness caused by the variation in Vth of TFTs.